December 30, 2011

Seeing the Unseen

image by Peter Grego, St Dennis, Cornwall, UK

On noticing the extremely good libration for the Moon’s southeastern limb it struck me that Vallis Schrödinger might possibly be visible, given the fact that illumination conditions were also ideal. On consulting LTVT this exceedingly elusive feature in the libration zone was predicted to be visible as a sliver of darkness at the limb. The LTVT simulation was used to prepare a cybersketch template to ensure positional accuracy; this was directly drawn over at the telescope eyepiece with features that were visible. The area chosen to portray included the southeastern limb, with most of Neumayer and Helmholtz (at the mid-left side) across to most of Gill (mid-right side); the craters at upper right include Gill C. Near the limb (left of centre, its own minor diameter away from limb), Hale was clearly visible as an individual crater. Along the limb was seen Sikorsky, the thin shadow cast by Vallis Schrödinger and its far eastern wall to a peak (presumably the rim of Moulton) near the right side. Orientation was difficult owing to the difference in appearance of the area compared to the mean view as presented in Rukl’s atlas, but consulting the Libration Zone V map made things clearer. Seeing conditions and the weather were not the best, and indeed cloud ended the session. The use of a binoviewer and erecting prism introduced a slight red fringe at the limb. However, the narrow shadow in Vallis Schrödinger’s interior was discerned. The portrayed profile of the limb is far from what I would consider a detailed and accurate representation; it was far more complicated than I have shown, with numerous additional minor bumps, but it is satisfactory enough to convey a general impression – my first of this particular feature. The observational cybersketch was retouched immediately after the observing session on the PC in PhotoPaint.